Unable to Export
An Internal Error has occurred: bad argument #1 to 'find' (string expected, got nil)
Using Windows 10 64x
The problem is likely caused by the Post-Processing/After Export: field being incorrectly left blank (by LR, not by the user). Simply put a valid action in that box, e.g. "Do Nothing" is fine, and the problem should go away.
As Don states it is an incorrect state of a setting the Export Window.
At the bottom are selections for "Post Processing Action", ensure it has a setting such as None....